This invention relates generally to air compression systems, and more specifically relates to a modular air compression system adapted for use with certain industrial processes, such as petrochemical processes.
In various chemical process applications, a requirement exists for providing compressed air for use in the particular processes and where more than one expansion is utilized. A typical application of a use for the modular system of the present invention is in the process for production of nitric acid, wherein as a part of the process, one may require admixing gaseous ammonia with compressed air, the mixed gases then being fed to a suitable catalytic reactor surface. After additional treament, the resulting oxides of nitrogen may be further reacted with compressed air (in the presence of water) to provide nitric acid. The compressed air similarly, may be used for additional reactive steps, or for other purposes as are required in the overall process. It, of course, will be understood that these indicated steps, are merely intended to represent typical steps in a plant operation in which the present apparatus may be used, and are set forth herein merely to illustrate the environment in which the present apparatus has application.
The typical chemical process for which the present invention is directed is, however, generally characterized by the need for compressed air for use in the process, and has available a hot expandable gas, typically hot tail gas resulting as a product of combustion and is depleted in oxygen content.
In conventional turbomachinery for such chemical processes, high power equipment, generally in excess of 1000 horsepower is provided in the form of individual compressors and individual steam and hot gas expanders. Such individual machines were generally installed as low speed, multi-train systems by laborious aligning of each machine, requiring extremely time-consuming, and often unreliable results. In addition, the multi-train systems inherently included a plurality of bearings through the multi-train by coupling individual two-bearing machines, and often necessitated an additional gear box or gearing to insure the correct speed of each unit.
A single shaft machine has been disclosed in U.S. Pat. No. 3,696,637 for low power applications in the cryogenic or refrigeration fields, however, its design is not feasible when considered for large power chemical processing applications where only recently have advances in high pressure ratio multistage compressors having a pressure ratio in excess of 4 to 1 and high speed radial inflow expanders having pressure ratios in excess of 5 to 1 made such a common shaft high power air compression module possible for the chemical processing industry.
In accordance with the foregoing, the present air compression system module provides a compact high speed, high power turbomachinery utilizing only two bearings which is readily applicable to a wide variety of chemical process applications. Because the system employs a single, common shaft, the module has high reliability and requires a minimum of maintenance. The module is preferably skid-mounted so as to preclude any problems of on-site alignment or assembly.
The elements of this modular air compression system include on a common power shaft, a multi-stage high pressure ratio compressor and two turboexpanders, one of the expanders being powered by steam and the other expander being powered by hot tail gas from the process itself. The multi-stage compressor is preferably a two-stage compressor wherein at least one of the two stages operates at a pressure ratio in excess of 4 to 1.